Cyanobiphenyl derivative, liquid crystal composition, liquid crystal element, and liquid crystal display device

ABSTRACT

A novel material for a liquid crystal composition that can be used for various liquid crystal devices is provided. A novel cyanobiphenyl derivative represented by General Formula (G1) is provided. In General Formula (G1), R 1  represents a single bond or a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms. Note that in General Formula (G1), R 1  may have a substituent. Examples of the substituent are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), a cyano group (CN), a trifluoromethylsulfonyl group (SO 2 CF 3 ), a trifluoromethyl group (CF 3 ), a nitro group (NO 2 ), an isothiocyanate group (NCS), and a pentafluorosulfanyl group (SF 5 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an object, a method, or a manufacturing method. In addition, the present invention relates to a process, a machine, manufacture, or a composition of matter. Specifically, one embodiment of the present invention relates to a semiconductor device, a display device, a driving method thereof, or a manufacturing method thereof. More specifically, one embodiment of the disclosed invention relates to a novel cyanobiphenyl derivative, a liquid crystal composition including the cyanobiphenyl derivative, a liquid crystal element in which the liquid crystal composition is used, a liquid crystal display device in which the liquid crystal composition is used, and manufacturing methods thereof.

2. Description of the Related Art

In recent years, liquid crystal has been used for a variety of devices; in particular, a liquid crystal display device (liquid crystal display) having features of thinness and lightness has been used for displays in a wide range of fields.

As the application field of a liquid crystal display device expands, various liquid crystal modes and liquid crystal compositions have been developed to improve the display quality (e.g., see Patent Documents 1 and 2).

REFERENCE Patent Document

[Patent Document 1] Japanese Published Patent Application No. H11-305187

[Patent Document 2] Japanese Published Patent Application No. 2003-238961

SUMMARY OF THE INVENTION

An object of one embodiment of the present invention is to provide a novel cyanobiphenyl derivative that can be used for various liquid crystal display devices. Another object is to provide a liquid crystal composition using the cyanobiphenyl derivative. Another object is to provide a liquid crystal element and a liquid crystal display device each including the liquid crystal composition. Another object is to provide a novel liquid crystal composition.

Note that the descriptions of these objects do not disturb the existence of other objects. In one embodiment of the present invention, there is no need to achieve all the objects. Other objects will be apparent from and can be derived from the description of the specification, the drawings, the claims, and the like.

One embodiment of the disclosed invention is a novel cyanobiphenyl derivative represented by General Formula (G1).

In General Formula (G1), R¹ represents a single bond or a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms.

Note that in General Formula (G1), R¹ may have a substituent. Examples of the substituent are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), a cyano group (CN), a trifluoromethylsulfonyl group (SO₂CF₃), a trifluoromethyl group (CF₃), a nitro group (NO₂), an isothiocyanate group (NCS), and a pentafluorosulfanyl group (SF₅).

Another embodiment of the present invention is a cyanobiphenyl derivative represented by Structural Formula (105).

Another embodiment of the present invention is a liquid crystal composition including a nematic liquid crystal and any one of cyanobiphenyl derivatives represented by General Formula (G1) and Structural Formula (105).

The cyanobiphenyl derivative of one embodiment of the present invention, which is represented by General Formula (G1) or Structural Formula (105), has an asymmetric center; therefore, when included in a liquid crystal composition, the cyanobiphenyl derivative can induce twisting of the liquid crystal composition to cause helical orientation. That is, the cyanobiphenyl derivative of one embodiment of the present invention can function as a chiral material in the liquid crystal composition.

Note that a chiral material has a function of twisting a liquid crystal molecule included in a liquid crystal composition. Indicators of the strength of twisting power include the helical pitch, the selective reflection wavelength, HTP (helical twisting power), and the diffraction wavelength.

In this specification and the like, a liquid crystal composition includes, in addition to the cyanobiphenyl derivative represented by General Formula (G1) or Structural Formula (105), a liquid crystalline compound and a non-liquid-crystalline compound. In particular, it is preferable that the liquid crystalline compound be a nematic liquid crystal. The non-liquid-crystalline compound may include, for example, a polymerizable monomer and/or a polymerization initiator.

The liquid crystal composition including the cyanobiphenyl derivative represented by General Formula (G1) or Structural Formula (105) as a chiral material can be used in a liquid crystal display device employing a lateral electric field mode such as a blue phase mode, a liquid crystal display device employing a vertical electric field mode such as a TN mode or a cholesteric liquid crystal mode, and the like. In particular, the cyanobiphenyl derivative represented by General Formula (G1) has a molecule structure that is partly common to that of a cyanobiphenyl-based liquid crystal compound; thus, a relatively large number of the cyanobiphenyl derivatives can be dissolved in the liquid crystal composition. Here, the liquid crystal composition needs to have strong twisting power for exhibiting a blue phase. The cyanobiphenyl derivative represented by General Formula (G1) can give strong twisting power to the liquid crystal composition by dissolving in the liquid crystal composition in quantity; thus, the cyanobiphenyl derivative represented by General Formula (G1) is preferably used as, in particular, a material for a liquid crystal composition that exhibits a blue phase.

One embodiment of the present invention includes, in its category, a liquid crystal element, and a liquid crystal display device and an electronic device each including the above liquid crystal composition.

One embodiment of the present invention can provide a novel cyanobiphenyl derivative that can be used for various liquid crystal display devices, a liquid crystal composition using the cyanobiphenyl derivative, a liquid crystal element and a liquid crystal display device each including the liquid crystal composition, or a novel liquid crystal composition.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are conceptual diagrams each illustrating a liquid crystal compound and a liquid crystal composition;

FIGS. 2A and 2B illustrate one mode of a liquid crystal display device;

FIGS. 3A to 3D each illustrate one mode of an electrode structure of a liquid crystal display device;

FIGS. 4A1, 4A2, and 4B illustrate liquid crystal display modules;

FIGS. 5A to 5F illustrate electronic devices;

FIGS. 6A and 6B are ¹H NMR charts of S-PP-O8CN;

FIG. 7 is a ¹H NMR chart of S-PP-O8CN; and

FIG. 8 shows spectra of intensities of reflected light from liquid crystal compositions in liquid crystal elements.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention disclosed in this specification will be described in detail below with reference to the accompanying drawings. Note that the invention disclosed in this specification is not limited to the following description, and it is easily understood by those skilled in the art that modes and details of the invention can be modified in various ways. Therefore, the invention disclosed in this specification is not construed as being limited to the description of the following embodiments or examples.

Embodiment 1

In this embodiment, a novel cyanobiphenyl derivative according to one embodiment of the present invention will be described.

One embodiment of the present invention is a cyanobiphenyl derivative represented by General Formula (G1).

In General Formula (G1), R¹ represents a single bond or a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms.

Note that in General Formula (G1), R¹ may have a substituent. Examples of the substituent are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), a cyano group (CN), a trifluoromethylsulfonyl group (SO₂CF₃), a trifluoromethyl group (CF₃), a nitro group (NO₂), an isothiocyanate group (NCS), and a pentafluorosulfanyl group (SF₅).

Specific examples of the cyanobiphenyl derivative represented by General Formula (G1) include cyanobiphenyl derivatives represented by Structural Formulae (100) to (110). Note that one embodiment of the present invention is not limited to these examples.

A variety of reactions can be used in a method for synthesizing the cyanobiphenyl derivative of this embodiment. An example of a method of synthesizing the cyanobiphenyl derivative represented by General Formula (G1) will be described below.

The cyanobiphenyl derivative represented by General Formula (G1) can be synthesized by a synthesis reaction shown by Reaction Formula (K-1).

By making Mitsunobu reaction of 4-cyano-4′-hydroxybiphenyl (Compound 1) with Compound 2, the cyanobiphenyl derivative represented by General Formula (G1), which is an objective substance, can be obtained (Reaction Formula (K-1)).

In General Formula (G1), R¹ represents a single bond or a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms.

Note that in General Formula (G1), R¹ may have a substituent. Examples of the substituent are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), a cyano group (CN), a trifluoromethylsulfonyl group (SO₂CF₃), a trifluoromethyl group (CF₃), a nitro group (NO₂), an isothiocyanate group (NCS), and a pentafluorosulfanyl group (SF₅).

As described above, the cyanobiphenyl derivative of one embodiment of the present invention can be synthesized.

The cyanobiphenyl derivative represented by General Formula (G1) has an asymmetric center; therefore, when included in a liquid crystal composition, the cyanobiphenyl derivative can induce twisting of the liquid crystal composition to cause helical orientation and can function as a chiral material.

The liquid crystal composition including the cyanobiphenyl derivative represented by General Formula (G1) as a chiral material can be used for a liquid crystal display device employing a vertical electric field mode such as a TN mode.

The structures, methods, and the like described in this embodiment can be combined as appropriate with any of the structures, methods, and the like described in the other embodiments.

Embodiment 2

In this embodiment, a liquid crystal composition including the cyanobiphenyl derivative described in Embodiment 1, which is one embodiment of the present invention, and a liquid crystal element or liquid crystal display device each including the liquid crystal composition will be described with reference to FIGS. 1A and 1B.

The liquid crystal composition of this embodiment includes at least a nematic liquid crystal and the cyanobiphenyl derivative described in Embodiment 1.

There is no particular limitation on the nematic liquid crystal included in the liquid crystal composition of one embodiment of the present invention, and examples thereof include a biphenyl-based compound, a terphenyl-based compound, a phenylcyclohexyl-based compound, a biphenylcyclohexyl-based compound, a phenylbicyclohexyl-based compound, a benzoic acid phenyl-based compound, a cyclohexyl benzoic acid phenyl-based compound, a phenyl benzoic acid phenyl-based compound, a bicyclohexyl carboxylic acid phenyl-based compound, an azomethine-based compound, an azo-based compound, an azoxy-based compound, a stilbene-based compound, a bicyclohexyl-based compound, a phenylpyrimidine-based compound, a biphenylpyrimidine-based compound, a pyrimidine-based compound, and a biphenyl ethyne-based compound.

FIGS. 1A and 1B illustrate examples of a liquid crystal element and a liquid crystal display device of one embodiment of the present invention.

Note that in this specification and the like, a liquid crystal element is an element which controls transmission or non-transmission of light by an optical modulation action of liquid crystal and includes at least a pair of electrode layers and a liquid crystal composition interposed therebetween. A liquid crystal element in this embodiment includes at least, between a pair of electrode layers (a pixel electrode layer 230 and a common electrode layer 232 having different potentials), a liquid crystal composition 208 which includes the cyanobiphenyl derivative represented by General Formula (G1) in Embodiment 1 and a nematic liquid crystal. Note that the liquid crystal composition 208 may include an organic resin.

FIGS. 1A and 1B each illustrate a liquid crystal element and a liquid crystal display device in which the liquid crystal composition 208 which includes a nematic liquid crystal and the cyanobiphenyl derivative represented by General Formula (G1) is provided between a first substrate 200 and a second substrate 201. A difference between the liquid crystal element and the liquid crystal display device in FIG. 1A and those in FIG. 1B is positions of the pixel electrode layer 230 and the common electrode layer 232 with respect to the liquid crystal composition 208.

In the liquid crystal element and the liquid crystal display device illustrated in FIG. 1A, the pixel electrode layer 230 and the common electrode layer 232 are provided to be adjacent to each other between the first substrate 200 and the liquid crystal composition 208. With the structure in FIG. 1A, a method in which the gray scale is controlled by generating an electric field substantially parallel (i.e., in a lateral direction) to a substrate to move liquid crystal molecules in a plane parallel to the substrate can be used.

For example, the liquid crystal composition is capable of quick response, and this can be favorably used for a successive additive color mixing method (a field sequential method) or a three-dimensional display method. In the successive additive color mixing method, light-emitting diodes (LEDs) of RGB or the like are arranged in a backlight unit and color display is performed by time division. In the three-dimensional display method, a shutter glasses system is used in which images for a right eye and images for a left eye are alternately viewed by time division.

In the liquid crystal element and the liquid crystal display device illustrated in FIG. 1B, the pixel electrode layer 230 and the common electrode layer 232 are provided on the first substrate 200 side and the second substrate 201 side, respectively, with the liquid crystal composition 208 interposed therebetween. With the structure in FIG. 1B, a method in which the gray scale is controlled by generating an electric field substantially perpendicular to a substrate to move liquid crystal molecules in a plane perpendicular to the substrate can be used. An alignment film 202 a may be provided between the liquid crystal composition 208 and the pixel electrode layer 230 and an alignment film 202 b may be provided between the liquid crystal composition 208 and the common electrode layer 232. A liquid crystal composition that includes the cyanobiphenyl derivative represented by General Formula (G1) according to one embodiment of the present invention and a nematic liquid crystal can be used in liquid crystal elements with a variety of structures and liquid crystal display devices in a variety of modes.

Although not illustrated in FIGS. 1A and 1B, an optical film such as a polarizing plate, a retardation plate, and an anti-reflection film, or the like is provided as appropriate. For example, circular polarization by the polarizing plate and the retardation plate may be used. In addition, a backlight or the like can be used as a light source.

In this specification, a substrate provided with a semiconductor element (e.g., a transistor) or a pixel electrode layer is referred to as an element substrate (a first substrate), and a substrate which faces the element substrate with a liquid crystal composition interposed therebetween is referred to as a counter substrate (a second substrate).

As a liquid crystal display device of one embodiment of the present invention, a transmissive liquid crystal display device in which display is performed by transmission of light from a light source, a reflective liquid crystal display device in which display is performed by reflection of incident light, or a transflective liquid crystal display device in which a transmissive type and a reflective type are combined can be provided.

In the case of the transmissive liquid crystal display device, a pixel electrode layer, a common electrode layer, a first substrate, a second substrate, and other components such as an insulating film and a conductive film, which are provided in a pixel region through which light is transmitted, have a property of transmitting light in the visible wavelength range.

On the other hand, in the case of the reflective liquid crystal display device, a reflective component which reflects light transmitted through the liquid crystal composition (e.g., a reflective film or substrate) may be provided on the side opposite to the viewing side of the liquid crystal composition. Therefore, a substrate, an insulating film, and a conductive film which are provided between the viewing side and the reflective component and through which light is transmitted have a light-transmitting property with respect to light in the visible wavelength range. Note that in this specification, a light-transmitting property refers to a property of transmitting at least light in the visible wavelength range. In the liquid crystal display device having the structure illustrated in FIG. 1B, the pixel electrode layer or the common electrode layer on the side opposite to the viewing side may have a light-reflecting property so that it can be used as a reflective component.

The pixel electrode layer 230 and the common electrode layer 232 may be formed with the use of one or more of the following: indium tin oxide (ITO); a conductive material in which zinc oxide (ZnO) is mixed into indium oxide; a conductive material in which silicon oxide (SiO₂) is mixed into indium oxide; indium oxide containing tungsten oxide; indium zinc oxide containing tungsten oxide; indium oxide containing titanium oxide; indium tin oxide containing titanium oxide; graphene; metals such as tungsten (W), molybdenum (Mo), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), cobalt (Co), nickel (Ni), titanium (Ti), platinum (Pt), aluminum (Al), copper (Cu), and silver (Ag); alloys thereof; and metal nitrides thereof.

As the first substrate 200 and the second substrate 201, a glass substrate of barium borosilicate glass, aluminoborosilicate glass, or the like, a quartz substrate, a plastic substrate, or the like can be used. Note that in the case of the reflective liquid crystal display device, a metal substrate such as an aluminum substrate or a stainless steel substrate may be used as a substrate on the side opposite to the viewing side.

With the use of the cyanobiphenyl derivative represented by General Formula (G1) as a chiral material in a liquid crystal composition, the amount of chiral material added to the liquid crystal composition can be small. Therefore, by using the liquid crystal composition for a liquid crystal element or a liquid crystal display device, a liquid crystal element or liquid crystal display device that can be driven at a low driving voltage can be provided, and a reduction in power consumption of the liquid crystal display device can be achieved.

The structures, methods, and the like described in this embodiment can be combined as appropriate with any of the structures, methods, and the like described in the other embodiments.

Embodiment 3

As a liquid crystal display device according to one embodiment of the present invention, a passive matrix liquid crystal display device and an active matrix liquid crystal display device can be provided. In this embodiment, an example of an active matrix liquid crystal display device according to one embodiment of the present invention will be described with reference to FIGS. 2A and 2B and FIGS. 3A to 3D.

FIG. 2A is a plan view of the liquid crystal display device and illustrates one pixel. FIG. 2B is a cross-sectional view taken along line X1-X2 in FIG. 2A.

In FIG. 2A, a plurality of source wiring layers (including a wiring layer 405 a) is arranged so as to be parallel to (extend in the vertical direction in the drawing) and apart from each other. A plurality of gate wiring layers (including a gate electrode layer 401) is provided to extend in a direction substantially perpendicular to the source wiring layers (the horizontal direction in the drawing) and to be apart from each other. Common wiring layers 408 are provided adjacent to the respective plurality of gate wiring layers and extend in a direction substantially parallel to the gate wiring layers, that is, in a direction substantially perpendicular to the source wiring layers (the horizontal direction in the drawing). A roughly rectangular space is surrounded by the source wiring layers, the common wiring layers 408, and the gate wiring layers. In this space, a pixel electrode layer and a common electrode layer of the liquid crystal display device are provided. A transistor 420 for driving the pixel electrode layer is provided at an upper left corner of the drawing. A plurality of pixel electrode layers and a plurality of transistors are arranged in matrix.

In the liquid crystal display device of FIGS. 2A and 2B, a first electrode layer 447 which is electrically connected to the transistor 420 serves as a pixel electrode layer, while a second electrode layer 446 which is electrically connected to the common wiring layer 408 serves as a common electrode layer. Note that a capacitor is formed by the first electrode layer and the common wiring layer. Although the common electrode layer can operate in a floating state (an electrically isolated state), the potential of the common electrode layer may be set to a fixed potential, preferably to a potential around a common potential (an intermediate potential of an image signal which is transmitted as data) in such a level as not to generate flickers.

A method in which the gray scale is controlled by generating an electric field substantially parallel (i.e., in a lateral direction) to a substrate to move liquid crystal molecules in a plane parallel to the substrate can be used. For such a method, an electrode structure used in an IPS mode as illustrated in FIGS. 2A and 2B and FIGS. 3A to 3D can be employed.

In a lateral electric field mode such as an IPS mode, for example, a first electrode layer (e.g., a pixel electrode layer a voltage of which is controlled in each pixel) and a second electrode layer (e.g., a common electrode layer to which a common voltage is supplied in all pixels), each of which has an opening pattern, are located below a liquid crystal composition. Therefore, the first electrode layer 447 and the second electrode layer 446, one of which is a pixel electrode layer and the other is a common electrode layer, are formed over a first substrate 441, and at least one of the first electrode layer and the second electrode layer is formed over an insulating film. The first electrode layer 447 and the second electrode layer 446 have a variety of shapes. For example, they can have an opening portion, a bent portion, a branched portion, or a comb-shaped portion. In order to generate an electric field substantially parallel to a substrate between the first electrode layer 447 and the second electrode layer 446, an arrangement is avoided in which they have the same shape and completely overlap with each other.

The first electrode layer 447 and the second electrode layer 446 may have a structure applicable in an FFS mode. In a lateral electric field mode such as an FFS mode, a first electrode layer (e.g., a pixel electrode layer a voltage of which is controlled in each pixel) having an opening pattern is located below a liquid crystal composition, and further, a second electrode layer (e.g., a common electrode layer to which a common voltage is supplied in all pixels) having a board shape is located below the opening pattern. In this case, the first electrode layer and the second electrode layer, one of which is a pixel electrode layer and the other of which is a common electrode layer, are formed over the first substrate 441, and the pixel electrode layer and the common electrode layer are stacked with an insulating film (or an interlayer insulating layer) interposed therebetween. One of the pixel electrode layer and the common electrode layer is formed below the insulating film (or the interlayer insulating layer) and has a board shape, whereas the other is formed above the insulating film (or the interlayer insulating layer) and has various shapes including an opening portion, a bent portion, a branched portion, or a comb-like portion. In order to generate an electric field slant to a substrate between the first electrode layer 447 and the second electrode layer 446, an arrangement is avoided in which they have the same shape and completely overlap with each other.

The liquid crystal composition including the cyanobiphenyl derivative represented by General Formula (G1) shown in Embodiment 1 and a nematic liquid crystal is used as a liquid crystal composition 444. The liquid crystal composition 444 may further include an organic resin.

With an electric field generated between the first electrode layer 447 that is the pixel electrode layer and the second electrode layer 446 that is the common electrode layer, liquid crystal of the liquid crystal composition 444 is controlled. An electric field in a lateral direction is formed for the liquid crystal, so that liquid crystal molecules can be controlled using the electric field.

FIGS. 3A to 3D show other examples of the first electrode layer 447 and the second electrode layer 446. As illustrated in top views of FIGS. 3A to 3D, first electrode layers 447 a to 447 d and second electrode layers 446 a to 446 d are arranged alternately. In FIG. 3A, the first electrode layer 447 a and the second electrode layer 446 a have a wavelike shape with curves. In FIG. 3B, the first electrode layer 447 b and the second electrode layer 446 b have a shape with concentric circular openings. In FIG. 3C, the first electrode layer 447 c and the second electrode layer 446 c have a comb-shape and partially overlap with each other. In FIG. 3D, the first electrode layer 447 d and the second electrode layer 446 d have a comb-shape in which the electrode layers are engaged with each other. In the case where the first electrode layers 447 a, 447 b, and 447 c overlap with the second electrode layers 446 a, 446 b, and 446 c, respectively, as illustrated in FIGS. 3A to 3C, an insulating film is formed between the first electrode layer 447 and the second electrode layer 446 so that the first electrode layer 447 and the second electrode layer 446 are formed over different films.

Since the second electrode layer 446 has an opening pattern, it is illustrated as a divided plurality of electrode layers in the cross-sectional view of FIG. 2B. The same applies to the other drawings of this specification.

The transistor 420 is an inverted staggered thin film transistor in which the gate electrode layer 401, a gate insulating layer 402, a semiconductor layer 403, and wiring layers 405 a and 405 b which function as a source electrode layer and a drain electrode layer are formed over the first substrate 441 which has an insulating surface.

There is no particular limitation on a structure of a transistor that can be used for a liquid crystal display device disclosed in this specification. For example, a staggered type or a planar type having a top-gate structure or a bottom-gate structure can be employed. The transistor may have a single-gate structure in which one channel formation region is formed, a double-gate structure in which two channel formation regions are formed, or a triple-gate structure in which three channel formation regions are formed. Alternatively, the transistor may have a dual gate structure including two gate electrode layers positioned over and below a channel region with a gate insulating layer provided therebetween.

An insulating film 407 that is in contact with the semiconductor layer 403, and an insulating film 409 are provided to cover the transistor 420. An interlayer film 413 is stacked over the insulating film 409.

The first substrate 441 and a second substrate 442 that is a counter substrate are firmly attached to each other with a sealant with the liquid crystal composition 444 interposed therebetween. The liquid crystal composition 444 can be formed by a dispenser method (a dropping method), or an injection method by which a liquid crystal is injected using capillary action or the like after the first substrate 441 is attached to the second substrate 442.

As the sealant, typically, a visible light curable resin, a UV curable resin, or a thermosetting resin is preferably used. Typically, an acrylic resin, an epoxy resin, an amine resin, or the like can be used. Further, a filler or a coupling agent may be included in the sealant.

In this embodiment, a polarizing plate 443 a is provided on the outer side (on the side opposite to the liquid crystal composition 444) of the first substrate 441, and a polarizing plate 443 b is provided on the outer side (on the side opposite to the liquid crystal composition 444) of the second substrate 442. In addition to the polarizing plates, an optical film such as a retardation plate or an anti-reflection film may be provided. For example, circular polarization by the polarizing plate and the retardation plate may be used. Through the above-described process, a liquid crystal display device can be completed.

Although not illustrated, a backlight, a sidelight, or the like may be used as a light source. Light from the light source is emitted from the first substrate 441 (element substrate) side so as to pass through the second substrate 442 on the viewing side.

The first electrode layer 447 and the second electrode layer 446 can be formed using a light-transmitting conductive material such as indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, ITO, indium zinc oxide, indium tin oxide to which silicon oxide is added, or graphene.

The first electrode layer 447 and the second electrode layer 446 can be formed using one or more kinds selected from a metal such as tungsten (W), molybdenum (Mo), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), cobalt (Co), nickel (Ni), titanium (Ti), platinum (Pt), aluminum (Al), copper (Cu), or silver (Ag); an alloy thereof; and a nitride thereof.

A conductive composition containing a conductive high molecule (also referred to as a conductive polymer) can be used to form the first electrode layer 447 and the second electrode layer 446. As the conductive high molecule, what is called a π-electron conjugated conductive polymer can be used. Examples include polyaniline or a derivative thereof, polypyrrole or a derivative thereof, polythiophene or a derivative thereof, and a copolymer of two or more of aniline, pyrrole, and thiophene or a derivative thereof.

An insulating film serving as a base film may be provided between the first substrate 441 and the gate electrode layer 401. The gate electrode layer 401 can be formed to have a single-layer or layered structure using a metal material such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, or scandium, or an alloy material which contains any of these materials as its main component. A semiconductor film which is doped with an impurity element such as phosphorus and is typified by a polycrystalline silicon film, or a silicide film of nickel silicide or the like can also be used as the gate electrode layer 401. By using a light-blocking conductive film as the gate electrode layer 401, light from a backlight (light emitted through the first substrate 441) can be prevented from entering the semiconductor layer 403.

For example, the gate insulating layer 402 can be formed with the use of a silicon oxide film, a gallium oxide film, an aluminum oxide film, a silicon nitride film, a silicon oxynitride film, an aluminum oxynitride film, or a silicon nitride oxide film. Alternatively, a high-k material such as hafnium oxide, yttrium oxide, lanthanum oxide, hafnium silicate, hafnium aluminate, hafnium silicate to which nitrogen is added, or hafnium aluminate to which nitrogen is added may be used as a material for the gate insulating layer 402. The use of such a high-k material enables a reduction in gate leakage current.

Alternatively, the gate insulating layer 402 can be formed using a silicon oxide layer by a CVD method in which an organosilane gas is used. As an organosilane gas, a silicon-containing compound such as tetraethoxysilane (TEOS) (chemical formula: Si(OC₂H₅)₄), tetramethylsilane (TMS) (chemical formula: Si(CH₃)₄), tetramethylcyclotetrasiloxane (TMCTS), octamethylcyclotetrasiloxane (OMCTS), hexamethyldisilazane (HMDS), triethoxysilane (chemical formula: SiH(OC₂H₅)₃), or trisdimethylaminosilane (chemical formula: SiH(N(CH₃)₂)₃) can be used. Note that the gate insulating layer 402 may have a single layer structure or a layered structure.

A material of the semiconductor layer 403 is not limited to a particular material and may be determined in accordance with characteristics needed for the transistor 420, as appropriate. Examples of a material that can be used for the semiconductor layer 403 will be described.

The semiconductor layer 403 can be formed using the following material: an amorphous semiconductor formed by a chemical vapor deposition method using a semiconductor source gas typified by silane or germane or by a physical vapor deposition method such as sputtering; a polycrystalline semiconductor formed by crystallizing the amorphous semiconductor with the use of light energy or thermal energy; a microcrystalline semiconductor in which a minute crystalline phase and an amorphous phase coexist; or the like. The semiconductor layer can be formed by a sputtering method, an LPCVD method, a plasma CVD method, or the like.

A typical example of an amorphous semiconductor is hydrogenated amorphous silicon, while a typical example of a crystalline semiconductor is polysilicon and the like. Polysilicon (polycrystalline silicon) includes what is called high-temperature polysilicon that contains, as its main component, polysilicon formed at a process temperature of 800° C. or higher, what is called low-temperature polysilicon that contains, as its main component, polysilicon formed at a process temperature of 600° C. or lower, and polysilicon formed by crystallizing amorphous silicon by using an element that promotes crystallization, or the like. Needless to say, as described above, a microcrystalline semiconductor or a semiconductor which includes a crystal phase in part of a semiconductor layer can also be used.

Alternatively, an oxide semiconductor may be used. In that case, any of the following can be used for example: indium oxide, tin oxide, zinc oxide, an In—Zn-based oxide, a Sn—Zn-based oxide, an Al—Zn-based oxide, a Zn—Mg-based oxide, a Sn—Mg-based oxide, an In—Mg-based oxide, an In—Ga-based oxide, an In—Ga—Zn-based oxide (also referred to as IGZO), an In—Al—Zn-based oxide, an In—Sn—Zn-based oxide, a Sn—Ga—Zn-based oxide, an Al—Ga—Zn-based oxide, a Sn—Al—Zn-based oxide, an In—Hf—Zn-based oxide, an In—La—Zn-based oxide, an In—Ce—Zn-based oxide, an In—Pr—Zn-based oxide, an In—Nd—Zn-based oxide, an In—Sm—Zn-based oxide, an In—Eu—Zn-based oxide, an In—Gd—Zn-based oxide, an In—Tb—Zn-based oxide, an In—Dy—Zn-based oxide, an In—Ho—Zn-based oxide, an In—Er—Zn-based oxide, an In—Tm—Zn-based oxide, an In—Yb—Zn-based oxide, an In—Lu—Zn-based oxide, an In—Sn—Ga—Zn-based oxide, an In—Hf—Ga—Zn-based oxide, an In—Al—Ga—Zn-based oxide, an In—Sn—Al—Zn-based oxide, an In—Sn—Hf—Zn-based oxide, and an In—Hf—Al—Zn-based oxide. In addition, any of the above oxide semiconductors may contain an element other than In, Ga, Sn, and Zn, for example, SiO₂.

Here, for example, an In—Ga—Zn—O-based oxide semiconductor means an oxide semiconductor containing indium (In), gallium (Ga), and zinc (Zn), and there is no limitation on the composition thereof.

For the oxide semiconductor layer, a thin film expressed by a chemical formula InMO₃(ZnO)_(m) (m>0) can be used. Here, M denotes one or more metal elements selected from Ga, Al, Mn, and Co. For example, M may be Ga, Ga and Al, Ga and Mn, Ga and Co, or the like.

As the oxide semiconductor layer, a CAAC-OS (c-axis aligned crystalline oxide semiconductor) film can be used, for example.

The CAAC-OS film is one of oxide semiconductor films having a plurality of c-axis aligned crystal parts.

As a material of the wiring layers 405 a and 405 b serving as source and drain electrode layers, an element selected from Al, Cr, Ta, Ti, Mo, and W; an alloy containing any of the above elements as its component; and the like can be given. Further, in the case where heat treatment is performed, the conductive film preferably has heat resistance against the heat treatment.

The gate insulating layer 402, the semiconductor layer 403, and the wiring layers 405 a and 405 b serving as source and drain electrode layers may be successively formed without being exposed to the air. When the gate insulating layer 402, the semiconductor layer 403, and the wiring layers 405 a and 405 b are formed successively without being exposed to the air, an interface between the layers can be formed without being contaminated with atmospheric components or impurity elements floating in the air. Thus, variations in characteristics of transistors can be reduced.

Note that the semiconductor layer 403 is partly etched so as to have a groove (a depression portion).

As the insulating film 407 and the insulating film 409 which cover the transistor 420, an inorganic insulating film or an organic insulating film formed by a dry method or a wet method can be used. For example, it is possible to use a silicon nitride film, a silicon oxide film, a silicon oxynitride film, an aluminum oxide film, or a tantalum oxide film, which is formed by a CVD method, a sputtering method, or the like. Alternatively, an organic material such as polyimide, acrylic, benzocyclobutene-based resin, polyamide, or an epoxy resin can be used. Other than such organic materials, it is also possible to use a low-dielectric constant material (a low-k material), a siloxane-based resin, PSG (phosphosilicate glass), BPSG (borophosphosilicate glass), or the like. A gallium oxide film may also be used as the insulating film 407.

Note that the siloxane-based resin is a resin including a Si—O—Si bond formed using a siloxane-based material as a starting material. The siloxane-based resin may include as a substituent an organic group (e.g., an alkyl group or an aryl group) or fluorine. In addition, the organic group may include fluorine. A siloxane-based resin is applied by a coating method and baked; thus, the insulating film 407 can be formed.

Alternatively, the insulating film 407 and the insulating film 409 may be formed by stacking a plurality of insulating films formed using any of these materials. For example, the insulating film 407 and the insulating film 409 may each have such a structure that an organic resin film is stacked over an inorganic insulating film.

In the above manner, by using the liquid crystal composition including the cyanobiphenyl derivative represented by General Formula (G1) and a nematic liquid crystal in a liquid crystal element or a liquid crystal display device, the liquid crystal element or the liquid crystal display device can be driven at a low driving voltage. Thus, a reduction in power consumption of the liquid crystal display device can be achieved.

The structures, methods, and the like described in this embodiment can be combined as appropriate with any of the structures, methods, and the like described in the other embodiments.

Embodiment 4

A liquid crystal display device having a display function can be manufactured by manufacturing transistors and using the transistors in a pixel portion and further in a driver circuit. Further, part or the whole of the driver circuit can be formed over the same substrate as the pixel portion, using the transistor, whereby a system-on-panel can be obtained.

The liquid crystal display device includes a liquid crystal element (also referred to as a liquid crystal display element) as a display element.

Further, a liquid crystal display module includes a panel in which a display element is sealed (a liquid crystal display device), and a component in which an IC or the like including a controller is mounted to the panel. One embodiment of the present invention also relates to an element substrate, which corresponds to one mode before the display element is completed in a manufacturing process of the liquid crystal display device, and the element substrate is provided with a means for supplying current to the display element in each of a plurality of pixels. Specifically, the element substrate may be in a state in which only a pixel electrode of the display element is provided, a state after formation of a conductive film to be a pixel electrode and before etching of the conductive film to form the pixel electrode, or any other states.

Note that a liquid crystal display device in this specification means an image display device or a light source (including a lighting device). Furthermore, a liquid crystal display device also refers to all the following display modules in some cases: a display module in which a connector, for example, a flexible printed circuit (FPC) or a tape carrier package (TCP) is attached to a liquid crystal display device, a display module in which a printed wiring board is provided at an end of a TCP, and a display module in which an integrated circuit (IC) is directly mounted on a liquid crystal display device by a chip on glass (COG) method.

The display module may include a touch sensor panel provided over the liquid crystal display device. Note that a panel for a touch sensor is not necessarily provided separately; the display module may include an in-cell or on-cell touch sensor panel in which, for example, an electrode for a touch sensor is provided on a counter substrate of the liquid crystal display device. Furthermore, the display module may include a backlight, an optical film (a polarizing plate, a retardation plate, or a luminance increasing film), and the like.

The appearance and a cross section of a liquid crystal display panel (a display module) which corresponds to a liquid crystal display device of one embodiment of the present invention will be described with reference to FIGS. 4A1, 4A2, and 4B. FIGS. 4A1 and 4A2 are top views of a panel in which transistors 4010 and 4011 and a liquid crystal element 4013 which are formed over a first substrate 4001 are sealed between the first substrate 4001 and a second substrate 4006 with a sealant 4005. FIG. 4B is a cross-sectional view taken along M-N of FIGS. 4A1 and 4A2.

The sealant 4005 is provided so as to surround a pixel portion 4002 and a scan line driver circuit 4004 which are provided over the first substrate 4001. The second substrate 4006 is provided over the pixel portion 4002 and the scan line driver circuit 4004. Thus, the pixel portion 4002 and the scan line driver circuit 4004 are sealed together with a liquid crystal composition 4008, by the first substrate 4001, the sealant 4005, and the second substrate 4006.

In FIG. 4A1, a signal line driver circuit 4003 that is formed using a single crystal semiconductor film or a polycrystalline semiconductor film over a substrate separately prepared is mounted in a region that is different from the region surrounded by the sealant 4005 over the first substrate 4001. FIG. 4A2 illustrates an example in which part of a signal line driver circuit is formed with the use of a transistor which is provided over the first substrate 4001. A signal line driver circuit 4003 b is formed over the first substrate 4001 and a signal line driver circuit 4003 a which is formed using a single crystal semiconductor film or a polycrystalline semiconductor film is mounted over a substrate separately prepared.

Note that there is no particular limitation on the connection method of a driver circuit which is separately formed, and a COG method, a wire bonding method, a TAB method, or the like can be used. FIG. 4A1 illustrates an example of mounting the signal line driver circuit 4003 by a COG method, and FIG. 4A2 illustrates an example of mounting the signal line driver circuit 4003 by a TAB method.

The pixel portion 4002 and the scan line driver circuit 4004 provided over the first substrate 4001 include a plurality of transistors. FIG. 4B illustrates the transistor 4010 included in the pixel portion 4002 and the transistor 4011 included in the scan line driver circuit 4004, as an example. An insulating layer 4020 and an interlayer film 4021 are provided over the transistors 4010 and 4011.

Any of the transistors shown in Embodiment 3 can be used as the transistors 4010 and 4011.

Further, a conductive layer may be provided over the interlayer film 4021 or the insulating layer 4020 so as to overlap with a channel formation region of a semiconductor layer of the transistor 4011 for the driver circuit. The conductive layer may have the same potential as or a potential different from that of a gate electrode layer of the transistor 4011 and can function as a second gate electrode layer. Further, the potential of the conductive layer may be GND, or the conductive layer may be in a floating state.

A pixel electrode layer 4030 and a common electrode layer 4031 are provided over the interlayer film 4021, and the pixel electrode layer 4030 is electrically connected to the transistor 4010. The liquid crystal element 4013 includes the pixel electrode layer 4030, the common electrode layer 4031, and the liquid crystal composition 4008. Note that a polarizing plate 4032 a and a polarizing plate 4032 b are provided on the outer sides of the first substrate 4001 and the second substrate 4006, respectively.

A liquid crystal composition including the cyanobiphenyl derivative represented by General Formula (G1) shown in Embodiment 1 and a nematic liquid crystal is used as the liquid crystal composition 4008. The structures of the pixel electrode layer and the common electrode layer described in any of the above embodiments can be used for the pixel electrode layer 4030 and the common electrode layer 4031.

With an electric field generated between the pixel electrode layer 4030 and the common electrode layer 4031, liquid crystal of the liquid crystal composition 4008 is controlled. An electric field in a lateral direction is formed for the liquid crystal, so that liquid crystal molecules can be controlled using the electric field.

As the first substrate 4001 and the second substrate 4006, glass, plastic, or the like having a light-transmitting property can be used. As plastic, a fiber-reinforced plastics (FRP) plate, a poly(vinyl fluoride) (PVF) film, a polyester film, or an acrylic resin film can be used. In addition, a sheet with a structure in which an aluminum foil is interposed between PVF films or polyester films can be used.

A columnar spacer denoted by reference numeral 4035 is obtained by selective etching of an insulating film and is provided in order to control the thickness (a cell gap) of the liquid crystal composition 4008. Alternatively, a spherical spacer may also be used. In the liquid crystal display device including the liquid crystal composition 4008, the cell gap which is the thickness of the liquid crystal composition is preferably greater than or equal to 1 μm and less than or equal to 20 μm. In this specification, the thickness of a cell gap refers to the length (film thickness) of a thickest part of a liquid crystal composition.

Although FIGS. 4A1, 4A2, and 4B illustrate examples of transmissive liquid crystal display devices, one embodiment of the present invention can also be applied to a transflective liquid crystal display device and a reflective liquid crystal display device.

In the example of the liquid crystal display device illustrated in FIGS. 4A1, 4A2, and 4B, the polarizing plate is provided on the outer side (the viewing side) of the substrate; however, the polarizing plate may be provided on the inner side of the substrate. The position of the polarizing plate may be determined as appropriate depending on the material of the polarizing plate and conditions of the manufacturing process. Furthermore, a light-blocking layer serving as a black matrix may be provided.

A color filter layer or a light-blocking layer may be formed as part of the interlayer film 4021. In FIGS. 4A1, 4A2, and 4B, a light-blocking layer 4034 is provided on the second substrate 4006 side so as to cover the transistors 4010 and 4011. With the provision of the light-blocking layer 4034, the contrast can be increased and the transistors can be stabilized more.

In FIG. 4B, the transistors 4010 and 4011 may be, but is not necessarily, covered with the insulating layer 4020 which functions as a protective film of the transistors. Note that the protective film is provided to prevent entry of contaminant impurities such as organic substance, metal, or moisture existing in the air and is preferably a dense film. For example, the protective film may be formed by a sputtering method to have a single-layer structure or a layered structure including any of a silicon oxide film, a silicon nitride film, a silicon oxynitride film, a silicon nitride oxide film, an aluminum oxide film, an aluminum nitride film, an aluminum oxynitride film, and an aluminum nitride oxide film.

Furthermore, a light-transmitting insulating layer may be further formed as a planarizing insulating film.

For the pixel electrode layer 4030 and the common electrode layer 4031, a light-transmitting conductive material can be used.

Further, a variety of signals and potentials are supplied to the signal line driver circuit 4003 which is separately formed, the scan line driver circuit 4004, or the pixel portion 4002 from an FPC 4018.

Further, since the transistor is easily broken by static electricity or the like, a protection circuit for protecting the driver circuits is preferably provided over the same substrate as a gate line or a source line. The protection circuit is preferably formed using a nonlinear element.

In FIGS. 4A1, 4A2, and 4B, a connection terminal electrode 4015 is formed using the same conductive film as that of the pixel electrode layer 4030, and a terminal electrode 4016 is formed using the same conductive film as that of source and drain electrode layers of the transistors 4010 and 4011.

The connection terminal electrode 4015 is electrically connected to a terminal included in the FPC 4018 via an anisotropic conductive film 4019.

Although FIGS. 4A1, 4A2, and 4B illustrate an example in which the signal line driver circuit 4003 is formed separately and mounted on the first substrate 4001, one embodiment of the present invention is not limited to this structure. The scan line driver circuit may be separately formed and then mounted, or only part of the signal line driver circuit or part of the scan line driver circuit may be separately formed and then mounted.

In the above manner, the liquid crystal composition including the cyanobiphenyl derivative represented by General Formula (G1) and a nematic liquid crystal can be used in a liquid crystal element or a liquid crystal display device.

The structures, methods, and the like described in this embodiment can be combined as appropriate with any of the structures, methods, and the like described in the other embodiments.

Embodiment 5

A liquid crystal display device disclosed in this specification can be used for a variety of electronic appliances (including game machines). Examples of such electronic appliances include a television set (also referred to as a television or a television receiver), a monitor of a computer or the like, a camera such as a digital camera or a digital video camera, a digital photo frame, a mobile phone handset (also referred to as a mobile phone or a mobile phone device), a portable game machine, a personal digital assistant, an audio reproducing device, a large game machine such as a pinball machine, and the like.

FIG. 5A illustrates a laptop personal computer, which includes a main body 3001, a housing 3002, a display portion 3003, a keyboard 3004, and the like. The liquid crystal display device described in any of the above Embodiments is used for the display portion 3003, whereby a laptop personal computer with low power consumption can be provided.

FIG. 5B illustrates a personal digital assistant (PDA), which includes a main body 3021 provided with a display portion 3023, an external interface 3025, operation buttons 3024, and the like. A stylus 3022 is included as an accessory for operation. The liquid crystal display device described in any of the above Embodiments is used for the display portion 3023, whereby a personal digital assistant with low power consumption can be provided.

FIG. 5C illustrates an e-book reader, which includes two housings, a housing 2701 and a housing 2703. The housing 2701 and the housing 2703 are combined with a hinge 2711 so that the e-book reader can be opened and closed with the hinge 2711 as an axis. With such a structure, the e-book reader can operate like a paper book.

A display portion 2705 and a display portion 2707 are incorporated in the housing 2701 and the housing 2703, respectively. The display portion 2705 and the display portion 2707 may display one image or different images. In the structure where different images are displayed in the above display portions, for example, the right display portion (the display portion 2705 in FIG. 5C) can display text and the left display portion (the display portion 2707 in FIG. 5C) can display images. The liquid crystal display device described in any of the above Embodiments is used for the display portions 2705 and 2707, whereby an e-book reader with low power consumption can be provided. In the case of using a transflective or reflective liquid crystal display device for the display portion 2705, the e-book reader may be used in a comparatively bright environment; accordingly, a solar cell may be provided so that power generation by the solar cell and charge by a battery can be performed. When a lithium ion battery is used as the battery, there are advantages of downsizing and the like.

FIG. 5C illustrates an example in which the housing 2701 is provided with an operation portion and the like. For example, the housing 2701 is provided with a power switch 2721, operation keys 2723, a speaker 2725, and the like. With the operation key 2723, pages can be turned. Note that a keyboard, a pointing device, or the like may also be provided on the surface of the housing, on which the display portion is provided. Furthermore, an external connection terminal (an earphone terminal, a USB terminal, or the like), a recording medium insertion portion, and the like may be provided on the back surface or the side surface of the housing. Further, the e-book reader may have a function of an electronic dictionary.

The e-book reader may transmit and receive data wirelessly. Through wireless communication, desired book data or the like can be purchased and downloaded from an electronic book server.

FIG. 5D illustrates a mobile phone, which includes two housings, a housing 2800 and a housing 2801. The housing 2801 includes a display panel 2802, a speaker 2803, a microphone 2804, a pointing device 2806, a camera lens 2807, an external connection terminal 2808, and the like. The housing 2800 includes a solar cell 2810 for charging the mobile phone, an external memory slot 2811, and the like. Further, an antenna is incorporated in the housing 2801. The liquid crystal display device described in any of the above Embodiments is used for the display panel 2802, whereby a mobile phone with low power consumption can be provided.

Further, the display panel 2802 is provided with a touch panel. A plurality of operation keys 2805 which is displayed as images is illustrated by dashed lines in FIG. 5D. Note that a boosting circuit by which a voltage output from the solar cell 2810 is increased to be sufficiently high for each circuit is also included.

In the display panel 2802, the display direction can be appropriately changed depending on a usage pattern. Further, the mobile phone is provided with the camera lens 2807 on the same surface as the display panel 2802, and thus it can be used as a video phone. The speaker 2803 and the microphone 2804 can be used for videophone calls, recording and playing sound, and the like as well as voice calls. Further, the housings 2800 and 2801 which are developed as illustrated in FIG. 5D can overlap with each other by sliding; thus, the size of the mobile phone can be decreased, which makes the mobile phone suitable for being carried.

The external connection terminal 2808 can be connected to an AC adapter and various types of cables such as a USB cable, and charging and data communication with a personal computer are possible. Moreover, a large amount of data can be stored and can be moved by inserting a storage medium into the external memory slot 2811.

Further, in addition to the above functions, an infrared communication function, a television reception function, or the like may be provided.

FIG. 5E illustrates a digital video camera, which includes a main body 3051, a display portion 3057, an eyepiece 3053, an operation switch 3054, a display portion 3055, a battery 3056, and the like. The liquid crystal display device described in any of the above Embodiments is used for the display portion 3057 and the display portion 3055, whereby a digital video camera with low power consumption can be provided.

FIG. 5F illustrates a television device, which includes a housing 9601, a display portion 9603, and the like. The display portion 9603 can display images. Here, the housing 9601 is supported by a stand 9605. The liquid crystal display device described in any of the above Embodiments is used for the display portion 9603, whereby a television device with low power consumption can be provided.

The television device can be operated with an operation switch of the housing 9601 or a separate remote controller. Further, the remote controller may be provided with a display portion for displaying data output from the remote controller.

Note that the television device is provided with a receiver, a modem, and the like. With the use of the receiver, general television broadcasting can be received. Furthermore, when the television device is connected to a communication network by wired or wireless connection via the modem, one-way (from a transmitter to a receiver) or two-way (between a transmitter and a receiver, between receivers, or the like) data communication can be performed.

The structures, methods, and the like described in this embodiment can be combined as appropriate with any of the structures, methods, and the like described in the other embodiments.

Example 1

In this example, an example of synthesis of (S)-4-cyano-4′-(6-methyl-n-octyl-1-oxy)biphenyl (abbreviation: S-PP-O8CN), which is the cyanobiphenyl derivative represented by Structural Formula (105) in Embodiment 1, will be described.

Step 1: Method for Synthesizing (S)-4-cyano-4′-(6-methyl-n-octyl-1-oxy)biphenyl (abbreviation: S-PP-O8CN)

Into a 200-mL three-necked flask were put 1.3 g (6.4 mmol) of 4-cyano-4′-hydroxybiphenyl and 1.7 g (6.4 mmol) of triphenylphosphine. The mixture was degassed while being stirred under reduced pressure, and the air in the flask was replaced with nitrogen. To this mixture were added 0.76 g (5.3 mmol) of (S)-6-methyl-1-octanol and 46 mL of tetrahydrofuran (THF). To this mixture was added 2.9 mL (6.4 mmol) of a toluene solution of diethyl azodicarboxylate (2.2 mol/L) in a nitrogen atmosphere at 10° C. or lower, and the mixture was stirred at room temperature for 24 hours. The obtained mixture was stirred at 40° C. for five hours. The obtained mixture was diluted with about 50 mL of diethyl ether, and washed with a saturated aqueous solution of sodium hydrogen carbonate. The aqueous layer of the resulting mixture was subjected to extraction with diethyl ether. The extracted solution and the organic layer were combined, and the mixture was dried with magnesium sulfate.

This mixture was separated by gravity filtration, and the obtained filtrate was concentrated to give a white oily substance. This oily substance was purified by silica gel column chromatography (developing solvent: hexane and ethyl acetate (hexane:ethyl acetate=5:1)). The obtained fraction was concentrated and subjected to vacuum drying to give a colorless oily substance. This oily substance was purified by high performance liquid column chromatography (developing solvent: chloroform). The obtained fraction was concentrated to give 0.86 g of a white solid of (S)-4-cyano-4′-(6-methyl-n-octyl-1-oxy)biphenyl, which was a target substance, in a yield of 51%. A reaction scheme of Step 1 described above is shown in (E1-1).

This compound was identified as (S)-4-cyano-4′-(6-methyl-n-octyl-1-oxy)biphenyl (abbreviation: S-PP-O8CN), which was a target substance, by nuclear magnetic resonance (NMR).

¹H NMR data of the obtained substance, S-PP-O8CN, are as follows.

¹H NMR (CDC₃, 300 MHz): δ (ppm)=0.84-0.89 (m, 6H), 1.09-1.46 (m, 9H), 1.77-1.86 (m, 2H), 4.01 (t, 2H), 6.99 (d, 2H), 7.52 (d, 2H), 7.62-7.70 (m, 4H).

FIGS. 6A and 6B and FIG. 7 show the ¹H NMR charts. Note that FIG. 6B is an enlarged chart showing a range of 0 ppm to 5 ppm of FIG. 6A, and FIG. 7 is an enlarged chart showing a range of 5 ppm to 10 ppm of FIG. 6A. The measurement results show that S-PP-O8CN, which was a target substance, was obtained.

Furthermore, HTP of a liquid crystal composition which is a mixture of S-PP-O8CN synthesized in this example and a nematic liquid crystal was measured. The measurement was performed at room temperature by the Grandjean-Cano wedge method. Note that the mixture ratio of a nematic liquid crystal to S-PP-O8CN in a liquid crystal composition was 98.0 wt %: 2.0 wt % (=nematic liquid crystal: S-PP-O8CN. As the nematic liquid crystal, a mixed liquid crystal of a mixed liquid crystal E-8 (produced by LCC Corporation, Ltd.), 4-(trans-4-n-propylcyclohexyl)-3′,4′-difluoro-1,1′-biphenyl (abbreviation: CPP-3FF) (produced by Daily Polymer Corporation), and 4-n-pentylbenzoic acid 4-cyano-3-fluorophenyl ester (abbreviation: PEP-5CNF) (produced by Daily Polymer Corporation) was used. The mixture ratio was 40 wt %:30 wt %:30 wt % (=E-8: CPP-3FF:PEP-5CNF).

The measurement results show that the HTP of the liquid crystal composition including S-PP-O8CN made in this example was about 1.7 μm⁻¹, and S-PP-O8CN synthesized in this example functions as a chiral material in a liquid crystal composition.

A chiral material that makes the HTP of the liquid crystal composition 20 μm⁻¹ or lower is suitably used for the preparation of a TN-mode liquid crystal composition whose helical pitch is long. The relation between HTP (μm⁻¹), the amount of the chiral material (wt %), and the helical pitch (μm) is expressed by Formula (1). According to Formula (1), when the amount of the chiral material is determined in accordance with the helical pitch with a desired value, the amount of the chiral material that makes the HTP of the liquid crystal composition high can be small. On the other hand, when the amount of the liquid crystal composition is small, the amount of the chiral material is also small. Thus, an error in the amount of the chiral material largely affects the liquid crystal composition.

$\begin{matrix} {{H\; T\;{P\left( {\mu\; m^{- 1}} \right)}} = \frac{1}{\frac{{amount}\mspace{14mu}{of}\mspace{14mu}{chiral}\mspace{14mu}{material}\mspace{14mu}\left( {{wt}\mspace{14mu}\%} \right)}{100} \times \mspace{95mu}{helical}\mspace{14mu}{pitch}\mspace{14mu}({\mu m})}} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack \end{matrix}$

In general, a TN material has a helical pitch of approximately 50 μm to 200 μm. For example, when the helical pitch is set to 100 μm (acceptable error range: 10 μm) and a chiral material that makes the HTP of the liquid crystal composition 5 μm⁻¹ is used, the amount of the chiral material is 0.182 wt % to 0.222 wt %. Whereas, when a chiral material that makes the HTP of the liquid crystal composition 100 μm⁻¹ is used, the amount of the chiral material is as extremely small as 0.009 wt % to 0.011 wt %, in which case, it is difficult to adjust the amount of the chiral material. For this reason, a chiral material that makes the HTP of the liquid crystal composition 20 μm⁻¹ or lower is suitable for the preparation of a TN-mode liquid crystal composition.

Thus, S-PP-O8CN made in this example is found to be used favorably as a chiral material of a liquid crystal composition, in particular as a chiral material of a TN mode liquid crystal composition.

Example 2

In this example, a liquid crystal composition according to one embodiment of the present invention and a TN mode liquid crystal element including the liquid crystal composition were made, and the characteristics of the liquid crystal composition and the liquid crystal element were evaluated.

In the liquid crystal composition made in this example, a mixed liquid crystal ZLI-4792 (produced by Merck) was used as a nematic liquid crystal and (S)-4-cyano-4′-(6-methyl-n-octyl-1-oxy)biphenyl (abbreviation: S-PP-O8CN) whose synthesis method is shown in Example 1 was used as a chiral material. In the liquid crystal composition, the proportion of the chiral material S-PP-O8CN with respect to the nematic liquid crystal ZLI-4792 was 1.28 wt %.

The helical pitch of the liquid crystal composition made in this example was 55.1 μm, which was measured at room temperature by the Grandjean-Cano wedge method.

Then, the alignment in a transmissive TN cell before and after voltage application was observed. The TN cell was the cell for vertical electric field application with a cell thickness of 4 μm. The pixel electrode layer was formed using indium tin oxide containing silicon oxide (ITSO) by a sputtering method over each glass substrate. The thickness of the pixel electrode layer was 110 nm. Then, SE-6414 (produced by Nissan Chemical Industries, Ltd.) was applied as a horizontal alignment film over each of the two glass substrates with a spin coater, and was baked at 230° C. Next, rubbing treatment was performed with a rubbing apparatus, and spacers each with a diameter of 4 μm were dispersed over one of the substrates. A heat-curable sealing material was applied over the substrate over which the spacers were dispersed, and the two substrates were bonded to each other such that the rubbing directions of the substrates twist by 90°. The bonded substrates were subjected to heat treatment at 160° C. for 4 hours while being pressed with a pressure of 0.3 kgf/cm².

The substrates formed in the above manner were divided, and the liquid crystal composition was injected by an injecting method using capillary action, so that a liquid crystal element was made. The liquid crystal element was observed by crossed nicols observation with a polarizing microscope (MX-61L produced by Olympus Corporation), which showed that line defects due to a reverse twist were not generated at all and favorable alignment was obtained.

Next, voltage-transmittance characteristics of the liquid crystal element were measured with a RETS+VT measurement system (produced by Otsuka Electronics Co., Ltd.). The voltage was applied at 0.2 V intervals in the range of from 0 V to 10 V. After the measurement, crossed nicols observation with the polarizing microscope was performed again, which showed that line defects due to the reverse twist were not generated at all and favorable alignment was obtained also after the voltage application.

The above-described results indicate that the liquid crystal composition according to one embodiment of the present invention can also be used for a TN mode element by including the cyanobiphenyl derivative represented by General Formula (G1) as a chiral material.

Example 3

In this example, one liquid crystal element was manufactured with the use of a liquid crystal composition including (S)-4-cyano-4′-(6-methyl-n-octyl-1-oxy)biphenyl (abbreviation: S-PP-O8CN) whose synthesis method is shown in Example 1 (Sample 1), and the other liquid crystal element was manufactured as a comparative example with the use of a liquid crystal composition in which the embodiment of the present invention is not used (Comparative Sample 1). Then, the characteristics thereof were evaluated.

Components of the liquid crystal compositions used in the liquid crystal elements in this example are listed in Table 1 (Sample 1) and Table 2 (Comparative Sample 1). The ratios (the mixture ratios) are all represented in weight ratios.

TABLE 1 Sample name Ratio (wt %) Sample 1 Liquid crystal 5CB 45.0 94 5CT 11.0 3OCB 16.0 5OCB 12.0 S-PP-O8CN 16.0 Chiral material S-DOL-Pn 6

TABLE 2 Sample name Ratio (wt %) Comparative Liquid crystal 5CB 45.0 94 Sample 1 5CT 11.0 3OCB 16.0 5OCB 12.0 8OCB 16.0 Chiral material S-DOL-Pn 6

Sample 1 and Comparative Sample 1 each were a mixture of liquid crystal and a chiral material. As a chiral material, (4S,5S)-4,5-bis [hydroxy-di(phenanthren-9-yl)]methyl-2,2-dimethyl-1,3-dioxolane (abbreviation: S-DOL-Pn) was used. As liquid crystal, 4-cyano-4′-n-pentylbiphenyl (abbreviation: 5CB) (produced by Tokyo Chemical Industry Co., Ltd.), 4-cyano-4′-(4-n-pentylphenyl)biphenyl (abbreviation: 5CT) (produced by LCC Corporation, Ltd.), 4-cyano-4′-(n-propyl-1-oxy)biphenyl (abbreviation: 3OCB) (produced by Wako Pure Chemical Industries, Ltd.), and 4-cyano-4′-(n-pentyl-1-oxy)biphenyl (abbreviation: 5OCB) (produced by Tokyo Chemical Industry Co., Ltd.) were used. In addition, as liquid crystal, S-PP-O8CN was used in Sample 1, and 4-cyano-4′-(n-octyl-1-oxy)biphenyl (abbreviation: 8OCB) (produced by Wako Pure Chemical Industries, Ltd.) was used in Comparative Sample 1.

The structural formulae of S-PP-O8CN, S-DOL-Pn, 5CB, 5CT, 3OCB, 5OCB, and 8OCB, which are used in this example, are shown below.

In this example, a liquid crystal element including Sample 1 as a liquid crystal composition and a liquid crystal element including Comparative Sample 1 as a liquid crystal composition were manufactured. Each liquid crystal element of this example was manufactured in such a manner that a glass substrate over which a pixel electrode layer and a common electrode layer were formed and a glass substrate serving as a counter substrate were bonded to each other using sealant with a space (4 μm) provided therebetween, and then each stirred liquid crystal composition of this example was injected between the substrates in an isotropic phase by an injection method.

The pixel electrode layer and the common electrode layer were formed using indium tin oxide containing silicon oxide (ITSO) by a sputtering method. The thickness of each of the pixel electrode layer and the common electrode layer was 110 nm, their widths were each 2 μm, and the distance between the pixel electrode layer and the common electrode layer was 2 μm. Further, an ultraviolet and heat curable sealing material was used for the sealant. As curing treatment, ultraviolet (irradiance of 100 mW/cm²) irradiation treatment was performed for 90 seconds, and then, heat treatment was performed at 120° C. for 1 hour.

Spectra of the intensities of reflected light from the liquid crystal compositions in the liquid crystal elements manufactured in this example were measured. For the measurement, a polarizing microscope (MX-61L produced by Olympus Corporation), a temperature controller (HCS302-MK1000 produced by Instec, Inc.), and a microspectroscope (LVmicroUV/VIS produced by Lambda Vision Inc.) were used.

In this example, the liquid crystal compositions in the liquid crystal elements were each made to be an isotropic phase. Then, the liquid crystal compositions were observed with a polarizing microscope while the temperature was decreased by 1.0° C. per minute with a temperature controller. In this manner, the temperature range where each liquid crystal composition exhibited a blue phase was measured. In Comparative Sample 1, the phase transition temperature between an isotropic phase and a blue phase was 68.2° C., and a phase transition temperature between a blue phase and a cholesteric phase was 64.2° C. In Sample 1, the phase transition temperature between an isotropic phase and a blue phase was 60.4° C., and a phase transition temperature between a blue phase and a cholesteric phase was 58.8° C.

Next, each liquid crystal element was set at a given constant temperature within the temperature range where each liquid crystal composition exhibits a blue phase, and the spectra of the intensities of reflected light from the liquid crystal compositions were measured with the microspectroscope.

Note that, in the measurement of the spectra of the intensities of reflected light in this example, a measurement mode of the microspectroscope was a reflective mode; polarizers were in crossed nicols; the measurement area was 12 μmφ; and the measurement wavelength was 250 nm to 800 nm. Since the measurement area was small, for the measurement, an area where the color of a blue phase had a long wavelength was determined with a monitor of the microspectroscope. Note that the measurement was performed from the side of the glass substrate serving as the counter substrate, over which the pixel electrode layer and the common electrode layer were not provided, in order to avoid an influence of the electrode layers in the measurement.

FIG. 8 shows the spectra of the intensities of reflected light from the liquid crystal compositions in the liquid crystal elements in this example. In each reflectance spectrum of the liquid crystal compositions, a peak of the diffraction wavelength was detected. The detected peak of the diffraction wavelength in the reflectance spectrum refers to the peak with the maximum value on the longest wavelength side. The vertical axis of the spectra indicates the intensity, and the spectrum is normalized by the reflected light intensity of the peak wavelength in each spectrum.

Note that the diffraction wavelength can be evaluated only in a blue phase, so that it is effective for evaluation of the twisting power of a blue phase. As the diffraction wavelength is on the shorter wavelength side, the liquid crystal composition has a smaller crystal lattice of a blue phase and stronger twisting power.

In the liquid crystal elements of this example, the peaks of the diffraction wavelengths on the longest wavelength sides in the reflectance spectra of the liquid crystal compositions were 396 nm in Sample 1 and 412 nm in Comparative Sample 1. As described above, even when 15 wt % or more of S-PP-O8CN is added instead of the liquid crystal material, the diffraction wavelength of the liquid crystal composition exhibiting a blue phase can be shorter without a 10° C. or more decrease in the temperature at which a blue phase is exhibited. As a result, light leakage due to the diffraction wavelength of the liquid crystal composition exhibiting a blue phase when no voltage is applied can be reduced, and a liquid crystal display device including the liquid crystal composition can have high contrast.

This application is based on Japanese Patent Application serial no. 2013-159196 filed with Japan Patent Office on Jul. 31, 2013, the entire contents of which are hereby incorporated by reference. 

What is claimed is:
 1. A compound represented by Formula (G1):

wherein R¹ represents a substituted C₁ to C₆ alkylene group, and wherein R¹ is substituted with a substituent selected from the group consisting of fluorine, chlorine, bromine, iodine, a cyano group, a trifluoromethylsulfonyl group, a trifluoromethyl group, a nitro group, an isothiocyanate group, and a pentafluorosulfanyl group.
 2. A liquid crystal composition comprising: the compound according to claim 1; and at least one of a polymerizable monomer and a polymerization initiator.
 3. A liquid crystal display device comprising the liquid crystal composition according to claim
 2. 4. A liquid crystal composition comprising the compound according to claim 1 and a nematic liquid crystal.
 5. A liquid crystal display device comprising the liquid crystal composition according to claim
 4. 